LAKE HERRING OF GREEN BAY, LAKE MICHIGAN 



103 



percent of the season's total. Growth started 

 sometime in May (this belief is supported by earlier 

 data on annulus formation) and for practical pur- 

 poses it was complete at the end of October. 



Hile (1936) made observations on midsummer 

 progress of the season's growth in cisco popula- 

 tions of four Wisconsin lakes by a procedure similar 

 to that just described. He found that growth had 

 been completed by the end of July in Trout Lake 

 and by the end of August in Muskellunge Lake, but 

 in Silver Lake only two-thirds to three-fourths of 

 the growth was completed in August. In Clear 

 Lake, males had completed 64 percent of their 

 season's growth in July and 81 percent in Septem- 

 ber and the females had completed 68 and 76 per- 

 cent, respectively, in these months. Although no 

 sex difTerence could be found in the progress of 

 growth of the Green Bay lake herring, the trend 

 did not differ greatly from that of the Clear Lake 

 stock. 



GROWTH CHARACTERISTICS OF LAKE 

 HERRING IN GREEN BAY 



Among the principal factors that must be con- 

 sidered in an analysis of the growth of lake herring 

 in Green Bay are sex differences, either natural 

 or resulting from selective destruction in the com- 

 mercial fishery; correlation of growth rate with 

 natural or fishery mortality; and geographical 

 variation within the bay. The influence of each 

 of these factors must be known in order to interpret 

 properly the growth of the entire population. 



Sex differences in growth 



Only one of four stocks of ciscoes from northern 

 Wisconsin lakes studied by Hile (1936) exhibited 

 sex difference in growth rate. No significant dif- 

 ferences in growth of males and females were found 

 by Carlander (1945), Cooper (1937), Eddy and 

 Carlander (1942), Stone (1938), or Van Oosten 

 (1929) in populations of lake herring studied by 

 them. Fry (1937, p. 65) did not discuss the influ- 

 ence of sex on growth rate but his data showed no 

 consistent differences in calculated growth of the 

 sexes up to age group VH beyond which males 

 tended to be larger. Since Van Oosten and Stone 

 used fish from pound nets, whereas the collections 

 of the other authors were taken with gill nets, it 

 appears that estimates of growth by males and 

 females are not distorted by collecting methods. 

 Differences in growth of the sexes in samples of 



the Green Bay lake herring population, though 

 occasionally large, were distributed irregularly, 

 showed no definite pattern, and favored neither 

 sex. They disappeared almost completely in the 

 best-represented age groups in the combined sam- 

 ples from pound nets (table 15) and gill nets 

 (table 16). The sexes are accordingly combined 

 in all subsequent treatment of growth data. 



Table 15. — Comparison of growth of mate and female lake 

 herring of age groups III and IV taken in pound nets, 

 1949-51 



[Calculated total length in inches] 



Table 16. — Comparison of growth of male and female lake 

 herring of age groups III and IV taken in gill nets, 

 1951-52 



[Calculated total length in inches] 



I Collected from 2-inch-mesh experimental gill nets. 



' Collected from 2H-inch and 2>4-inch-mesh commercial gill nets. 



Effect of gear selection on estimation of growth 



From a review of tlie literature and from his 

 own data Hile (1936, pp. 298, 306) held that— 

 * * * in general a sparse representation in a sample of a 

 young age group whose average length is near the lower limit of 

 effectiveness of the nets used, is a source of suspicion as to 

 the reliability of the sample of that particular group. If 

 this same sparsely represented group gives calculated 

 growths that are in serious disagreement with those of the 

 older age groups it should be eliminated from the data 

 used for the study of growth in the population as a whole. 



